1. Field of the Invention
The present invention relates to a stator winding which is suitable for use in a rotating electrical machine such as an electric motor or generator, and more specifically which is suitable for use in a slotless stator of a high speed rotating electrical machine, and to a manufacturing method therefor.
This application is based on Japanese Patent Application No. Hei 11-211395, the contents of which are incorporated herein by reference.
2. Description of the Related Art
Heretofore, there has been proposed a slotless stator where, from the viewpoint of making even the magnetic resistance of the main magnetic flux path as viewed from the stator side, a slot is not formed. A radial gap type slotless construction where cylindrical windings are secured to an inner peripheral side of a slotless stator which faces a rotor, is widely used.
Such a radial gap type slotless construction is disclosed in the specification of U.S. Pat. No. 5,313,131.
FIG. 13 is a perspective view showing an end portion of a slotless stator. A plurality of coil segments 103 are secured to an inner peripheral face of a stator core 101. These coil segments 103, as shown in FIG. 14, bear an approximate quadrilateral shape with rounded corners. When these coil segments 103 are used, this gives a construction, as can be seen from FIG. 13, where one side 105 of the quadrilateral shape is exposed from the edge portion of the stator core 101.
If one side of the coil segment is exposed, then the amount of the winding for that part is wastefully used. This increases the resistance value of the windings and produces heat. In the case where this is used in a high speed electric motor with the speed reaching for example several tens of thousand rpm, such heat cannot be disregarded.
Furthermore, if the number of turns of the coil is increased, then the amount exposed from the stator increases accordingly. Moreover, the less the number of poles the longer the span length exposed from the stator end. Furthermore, in coping with a high output brings the requirement for arranging conductors compatible with high currents. In such a case, the size of the coil in the axial direction or in the diametral direction is increased, so that the rotating electrical machine itself is enlarged. That is to say, there is the problem that when the conductor amount is increased to realize the high output, the rotating electrical machine is enlarged.
In particular, in the case where the stator coil is enlarged in the axial direction, then corresponding to this the rotor is also enlarged in the axial direction. This has a significant influence on the centrifugal strength and shaft vibration of the rotor. Consequently, there is a strong demand for miniaturizing the stator coil as much as possible particularly in the axial direction.
As another shape for the abovementioned approximate quadrilateral shape coil segment, there is proposed in Japanese Patent Application, Second Publication No. Sho 53-44362 a coil having rhombic shaped turns.
FIG. 15 shows a band shape coil 111 formed by sequentially aligning rhombic shaped turns. FIG. 16 shows a cylindrical shaped coil 113 formed by rolling the band shaped coiled 111 of FIG. 15. With such a cylindrical shaped 113, since apexes of the rhombic shapes are located at opposite ends of the cylindrical body, the amount of windings exposed from the stator can be kept to a minimum.
With the form of FIG. 15 however, the band shaped coil comprising rhombic shaped turns is formed from single wires, and is not possible to make this a multi-layered cylindrical coil which is a necessity in order to obtain a high output. In this case also, even if this is parallel connected, phase matching is difficult, and there is the problem that if these are laminated in several layers, the coil thickness increases.
Accordingly, the present invention takes into consideration the above problems with the object of providing a slotless stator which addresses the realization of high output and also miniaturization. Moreover, it is an object to provide a method of manufacturing a stator winding which is simple and has good formability.
The above objects are achieved by the following means.
The stator winding of the present invention is characterized in being a hollow cylindrical body formed by: forming turns by winding a wire sheaf of a plurality of fine wires composed of conductors bundled together, through one turn in an approximately rhombic shaped forming approximately rhombic shape coil segments comprising a continuous length of the wire sheaves by winding and arranging a plurality of the turns so as to be sequentially shifted continuously in a direction of one diagonal of the rhombic shaped, forming a band shape body using a plurality of the coil segments with these coil segments sequentially shifted in the direction of the one diagonal and so as to be adjacent to each other, and rolling the band shape body into a cylindrical shape.
Since the coil segments are each formed from a single wire sheaf comprising a plurality of fine wires, then compared to a coil segment formed a single wire, this can be made to cope with higher speed rotation. Moreover, with the wire sheaf, by pressing this using a press, an increase in the thickness of the coil can be avoided, and by twisting together, circulating current losses are reduced.
The wire sheaf is characterized in that one end portion of opposite end portions of the respective turns which are located in the direction of an other diagonal orthogonal to the direction of the one diagonal is wound from an inner peripheral side of the hollow cylindrical body to an outer peripheral side thereof, and the other end portion of the opposite end portions of the respective turns, is wound from the outer peripheral side of the hollow cylindrical body to the inner peripheral side thereof.
The respective turns are characterized in that opposite end portions thereof which are located in the direction of an other diagonal orthogonal to the direction of the one diagonal, have bent back portions which proceed so as to project to an outside of the turn, and then return back in an approximate U-shape and proceed so as to return to an inside.
By locating the bent back portions on the end portions of the hollow cylindrical body, these bent back portion face in the direction of the other diagonal of the rhombic shape, that is to say in the longitudinal (axis) direction of the hollow cylindrical body. As a result, the bent back portions can be compactly arranged around the circumferential direction of the hollow cylindrical body, so that a plurality of turns can be closely wound. Consequently, even if the number of turns is increased, the bent back portions are laminated side by side, and these bent back portions are not exposed extending in the radial direction or the axial direction of the cylindrical body.
When the windings according to the present invention are secured to the core of the slotless stator, only the bent back portions of the respective turns are exposed from the end of the stator. That is to say, the portion exposed from the core is only the bent back portions and is only a little, Hence the winding amount is considerably reduced of the entire windings.
Preferably the respective turns are arranged in a condition touching adjacent turns. In this way, a winding wound at a high density can be formed.
More preferably, of the four sides of the approximately rhombic shaped coil segments, two sides located on one side of the other diagonal are arranged on an inner peripheral side of the hollow cylindrical body, and the other two sides opposite to the two sides located on the one side are arranged on an outer peripheral side of the hollow cylindrical body.
Since two sides of the coil segment are arranged on the inner peripheral side of the hollow cylindrical body, and the other two sides are arranged on the outer peripheral side thereof, then on both the inner peripheral side and the outer peripheral side, the wire sheaves are closely arranged.
Even more preferably, the two sides of the coil segment which are arranged on the inner peripheral side of the hollow cylindrical body are abutted in the circumferential direction against the two sides which are arranged on the inner peripheral side of the adjacent coil segment, and the respective coil segments are arranged sequentially shifted while being overlapped so as to radially overlap the two sides of the adjacent coil segments, which are arranged on the outer peripheral side of the hollow cylindrical body.
The two side of the respective coil segments which are arranged on the inner peripheral side of the hollow cylindrical body are uniformly arranged in the circumferential direction. Furthermore, the two sides of the respective coil segments which are arranged on the outer peripheral side of the hollow cylindrical body overlap the two sides arranged on the inner peripheral side of the adjacent coil segment, in the radial direction of the hollow cylindrical body. In so doing, the respective coil segments are arranged in an alternately overlapped fashion. As a result, the plurality of coil segments are closely overlapped in the circumferential direction and the diametral direction.
More preferably, with the bent back portions located on the opposite ends of the respective turns, one end side thereof is bent from the inner peripheral side of the hollow cylindrical body towards the outer peripheral side, and/or the other end side is bent from the outer peripheral side towards the inner peripheral side.
Since the bent back portions are bent from the inner peripheral side (outer peripheral side) to the outer peripheral side (inner peripheral side), the bent back portions can be arranged closely in the circumferential direction. As a result, the respective turn sets can be arranged sequentially and in close contact in the circumferential direction. That is to say, even if the number of turns of increased, the winding is not enlarged in the axial direction and the diametral direction.
More preferably, the wire sheaf is twisted at least one turn in a helical form within a range of one side of the respective approximately rhombic shaped turns.
Twisting in a helical shape gives a construction the same as a Litz wire used for example in high frequency transformers. Hence the electromotive voltage difference which is produced in the respective strands in the wire sheaf forming the turns can be reduced, and the generation of unnecessary losses of, for example circulating currents can be suppressed.
More preferably, the wire sheaf has an approximately rectangular shape cross-section.
When wire sheaves having rectangular cross-sections are arranged adjacent to each other, these wire sheaves can be arranged in a close contact condition, thereby increasing the conductor space factor of the coil segment.
More preferably, the fine wires have a distorted circular cross-section with linear portions, and adjacent fine wires are contacted at the linear portions.
In this way, the conductor space factor is further increased.
A method of manufacturing a stator winding according to the present invention, which stator winding may be used in a rotating electric machine having a slotless stator, comprises steps of:
a turn forming step for forming turns by winding a wire sheaf of a plurality of fine wires composed of conductors bundled together, through one turn in an approximately rhombic shape; a coil segment forming step for forming coil segments comprising a continuous length of the wire sheaf by winding and arranging a plurality of the turns so as to be sequentially shifted continuously in the direction of one diagonal of the rhombic shape; and a hollow cylindrical body forming step for forming a band shaped body using a plurality of the coil segments by sequentially shifting and overlapping these coil segments so as to be adjacent in the direction of the one diagonal, and rolling the band shaped body into a hollow cylindrical shape. The turn forming step includes a step where, with the wire sheaf, one end portion of opposite end portions of the respective turns which are located in the direction of an other diagonal orthogonal to the direction of the one diagonal is wound from an inner peripheral side of the hollow cylindrical body to an outer peripheral side thereof, and an other end portion of the opposite end portions of the respective turns, is wound from the outer peripheral side of the hollow cylindrical body to the inner peripheral side thereof.
The turn forming step is characterized in incorporating a bent back portion forming step for forming bent back portions at opposite end portions of the respective turns which are located in the direction of the other diagonal orthogonal to the direction of the one diagonal, each said bent back portion proceeds so as to project to an outside of the turn, and then returns back in an approximate U-shape and proceeds so as to return to an inside of the turns.
Preferably, the turn forming step incorporates a press step for pressing the wire sheaf so that adjacent fine wires are closely contacted together.
By pressing, the respective fine wires constituting the wire sheaf are deformed to a close contact condition. Furthermore, by keeping the respective fine wires in a close contact condition in this way, the cross-sectional shape of the wire sheaf can be stably maintained.
More preferably, prior to the press step there is provided a step for twisting the wire sheaf at least one turn in a helical form within a range of one side of the approximately rhombic shaped turn.
By carry out pressing after applying a twist, the respective fine wires are deformed in a twisted condition, and hence a more rigid close contact condition is obtained.
More preferably, the press step incorporates a step for forming the wire sheaf so that the wire sheaf has an approximately rectangular cross-section.